Processing and recycling method of thermoplastic polyester elastomer

Abstract

The invention provides a processing and recycling method of a thermoplastic polyester elastomer. The method comprises the following steps: mixing a thermoplastic polyester elastomer with a chain extender for primary processing; crushing the recycled material obtained after the first processing, mixing the crushed recycled material with the new material according to a mass ratio of 10: 90-40: 60, and carrying out second processing; wherein the chain extender is a compound containing more than two functional groups capable of reacting with hydroxyl, or a mixture of the compounds, and preferably, the average functionality of the chain extender is 2-3. Compared with a conventional processing method in the prior art, the processing and recycling method of the thermoplastic polyester elastomer provided by the invention has the advantage that mechanical properties such as tearing strength of a product containing recycled materials are improved.

Description

Technical Field

[0001] The present invention relates to a processing and recycling method of thermoplastic polyester elastomer, belonging to the technical field of polymer materials. Background Art

[0002] Thermoplastic plastics, also known as thermosoftening plastics, refer to plastic polymer materials that become flexible or plastic when the temperature rises to a certain degree and solidify again after cooling. Thermoplastic plastics soften and flow when heated and harden when cooled, and this process is reversible and can be repeated.

[0003] Most polyester resins are thermoplastic materials. Thermoplastic polyesters are usually sold in the form of polyester resin particles, and downstream processing manufacturers can use various convenient processing means such as injection molding and extrusion to process the resin particles. During the processing, thermoplastic polyesters need to experience high temperature, high shear environment, and may also be in an environment with oxygen, water vapor, etc., which will cause molecular chain breakage, molecular weight reduction and product performance degradation. The main factors leading to molecular chain breakage in polyesters include hydrolysis, oxidation, shear, etc. The industrial community has fully recognized this problem and has corresponding solutions to a certain extent. In order to reduce hydrolysis, it is recommended to dry thermoplastic polyesters before use, which is common knowledge in the industry and will not be elaborated here.

[0004] CN1969012A discloses adding various resins and additives to polyester resin to obtain a composite, thereby improving physical properties and reducing costs. Specifically, a hydrolysis inhibitor such as polycarbodiimide is added, and the main purpose is to overcome the problem of the hydrolysis tendency of the polyester resin and avoid the decline of mechanical properties during the processing. Even with the above method, molecular chain breakage, molecular weight reduction and product performance degradation still objectively exist. Especially for thermoplastic polyesters, the scraps, tailings and defective products generated during the processing stage need to be crushed into recycled materials for reuse. The molecular weight of these recycled materials (or secondary materials) is usually lower than that of the new materials (or primary materials), and the performance of the products is also inferior to that of the corresponding products made of new materials. The technical solution adopted is a preventive or on-site remedial idea.

[0005] One of the common treatment methods in the industry is to blend the recycled materials with the new materials in a certain proportion and then reuse them to control the performance degradation within a certain range. The advantage of this method is simplicity and feasibility, and the disadvantage is that degradation still exists. Especially after multiple reuses, a significant amount of oligomer small molecules will be introduced, resulting in a significant decline in performance. For some high-value-added and high-performance materials such as thermoplastic polyester elastomer (TPEE), a solution to improve the performance of recycled materials by paying a small cost is urgently needed by application manufacturers.

[0006] JP2011084616A discloses a modified recycled polyester resin, which is modified by adding a modifier having epoxy groups and oxazoline groups to the recycled polyester resin. The molar ratio of the oxazoline groups to the epoxy groups of the modifier is oxazoline groups:epoxy groups = 100:90 - 100:0.01, and the addition amount of the modifier is 0.001 - 15 parts by mass per 100 parts by mass of the recycled PET resin. The chemical principle of this method is to promote the reaction of carboxyl groups, and the source of the carboxyl groups is mainly generated in the previous processing. This method adopts the idea of post-remedy.

[0007] However, there are still certain problems with the relevant properties of the thermoplastic polyester elastomer obtained after recycling in the current technical solutions. Summary of the Invention

[0008] To solve the above technical problems, the object of the present invention is to provide a processing and recycling method for a thermoplastic polyester elastomer, which is a preventive adjustment in the processing stage to improve the molecular weight of polyester polymers in the recycled materials of the finished products and improve the performance of the finished products blended with the recycled materials, namely a TPEE recycling solution.

[0009] To achieve the above object, the present invention provides a processing and recycling method for a thermoplastic polyester elastomer, which includes the following steps:

[0010] Mix the thermoplastic polyester elastomer with a chain extender for the first processing;

[0011] Crush the recycled materials obtained after the first processing, and mix them with new materials in a mass ratio of 10:90 - 40:60 for the second processing;

[0012] Wherein, the chain extender refers to a compound containing more than 2 functional groups capable of reacting with hydroxyl groups or a mixture of such compounds.

[0013] According to the specific implementation scheme of the present invention, for thermoplastic polyesters, the recycled materials refer to scraps, tailings, defective products, etc. generated in the processing stage. These all need to be crushed into recycled materials for reuse. The molecular weight of these recycled materials (or secondary materials) is usually lower than that of the new materials (i.e., new materials of thermoplastic polyester elastomers, or primary materials, namely thermoplastic polyester elastomers that have not been processed by thermoplastic materials such as extrusion and injection molding), and the performance of the products is also inferior to that of the products corresponding to the new materials.

[0014] In the process of extrusion or injection molding (the first processing) of the products of the present invention, the carboxyl groups or hydroxyl groups remaining at the ends of the polyester polymers can react with the chain extender to increase the molecular weight of the products. Therefore, even after the degradation during the processing process, the products can still have a relatively high molecular weight and maintain their necessary mechanical properties, etc.

[0015] According to the specific embodiments of the present invention, the chain extender used in the present invention preferably has functional groups that can react with carboxyl groups or hydroxyl groups, have no by-products, and have a fast reaction rate. In processing equipment such as extruders and injection molding grades, the residence time of the resin is very short, so a fast reaction rate and extremely high efficiency are required. Epoxy groups and isocyanate groups have the advantages of high reaction activity and no small molecule by-products, so they are preferably selected. In order to facilitate feeding and rapid mixing, a chain extender with a molecular weight ≤ 1000 is preferably used, and the chain extender is preferably a liquid.

[0016] According to the specific embodiments of the present invention, if the average functionality of the chain extender is less than 2, chain extension cannot be achieved; if the average functionality of the chain extender is higher than 3, gelation is likely to occur. Preferably, the average functionality of the chain extender is 2-3, and more preferably 2. Selecting a chain extender with a functionality of 2 can ensure the thermoplasticity of the recycled material. For chain extenders with a functionality higher than 2, the dosage and reaction time need to be appropriately controlled during use.

[0017] According to the specific embodiments of the present invention, preferably, 0.3-3 parts by mass of the chain extender is added to every 100 parts by mass of the thermoplastic polyester elastomer.

[0018] According to the specific embodiments of the present invention, preferably, the method further includes: adding a chain extender to the mixture of the recycled material and the thermoplastic polyester elastomer before the second processing. More preferably, 0.3-3 parts by mass of the chain extender is added to every 100 parts by mass of the mixture of the recycled material and the thermoplastic polyester elastomer.

[0019] According to the specific embodiments of the present invention, preferably, the functional groups capable of reacting with hydroxyl groups are epoxy groups and / or isocyanate groups. Among them, when the functional groups capable of reacting with hydroxyl groups are epoxy groups, preferably, the chain extender is one or a combination of two or more of bisphenol A diglycidyl ether, ethylene glycol diglycidyl ether, and butanediol diglycidyl ether. When the functional groups capable of reacting with hydroxyl groups are isocyanate groups, preferably, the chain extender is one or a combination of two or more of dimethylene polyphenyl polyisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).

[0020] According to the specific embodiments of the present invention, preferably, the first processing includes processing methods for thermoplastic materials such as injection molding and / or extrusion.

[0021] According to the specific embodiments of the present invention, preferably, the second processing includes processing methods for thermoplastic materials such as injection molding and / or extrusion.

[0022] The processing method of the present invention is not limited to extrusion or injection molding. Only these two processing methods are cited in the present invention because they are common and easy to compare performance. Those skilled in the art can easily extend to other specific processing means when understanding the technical solution of the present invention.

[0023] According to a specific embodiment of the present invention, preferably, the method further includes: the step of adding other resins and / or additives to the thermoplastic polyester elastomer before the first processing; and / or, the step of adding other resins and / or additives to the mixture of the recycled material and the new material before the second processing.

[0024] The inventors of the present invention verified the technology in the existing solutions and found that when the recycled material of untreated TPEE (thermoplastic polyester elastomer) is added to the new material for processing and molding, it will cause a decrease in performance (mainly the decrease in tensile strength and tear strength), and this phenomenon is as expected. If the improved method of first blending the recycled material and the new material in a certain proportion, adding a chain extender such as a polyfunctional epoxide compound or a polyfunctional isocyanate compound at the same time, and then performing processing such as extrusion or injection molding, and chain extension occurs during the processing, when the mass fraction of the recycled material is <5%, relatively good results can be obtained by adjusting the dosage of the chain extender and the processing conditions, and the mechanical properties and processing properties of the product are not much different from those of 100% new material. However, when the mass fraction of the recycled material is 10 - 40%, even if a large amount of chain extender is added and different combinations of chain extenders are tried, a decrease in mechanical properties, especially the decrease in tear strength, is still observed. The present invention attempts several methods for improving recycled materials in the prior art. Although the performance of the recycled material can be improved compared with not using the corresponding prior art method, the improvement effect on the mechanical properties, especially the tear strength, is not good when the recycled material and the new material are blended in proportion.

[0025] In this regard, the inventors of the present invention conducted experimental research: First, the new material was mixed with a small amount of color masterbatch and then injection-molded. The injection-molded spline was crushed to obtain recycled material showing blue color, and the basic properties such as the molecular weight, intrinsic viscosity, and melt index of the recycled material were tested. Blue was selected because the new material is generally off-white and is easy to distinguish from blue. Then, the blue recycled material and the new material were mixed in different mass ratios of 10:90 - 40:60 and injection-molded to obtain splines of the recycled material. Observation of the recycled material samples found that under the existing injection-molding conditions, the recycled material and the new material were not fully and completely mixed, and there were regions where the recycled material was concentrated. Further testing of the mechanical properties found that especially the tear strength was greatly affected by the test site. When the test site was in the region where the recycled material was concentrated, an obvious decrease in tear strength was observed, with the maximum decrease reaching 30%. Thus, it was determined that the main reason for the decrease in mechanical properties was the influence of the recycled material. Under the existing injection-molding conditions, the reason why the recycled material and the new material were not fully and completely mixed might be that the molecular weight and viscosity of the recycled material were smaller than those of the new material. Therefore, the melting and rheological properties were inconsistent with those of the new material, and there was a tendency to aggregate.

[0026] On this basis, the inventors of the present invention tried several methods for improving recycled materials in the prior art, such as adding chain extenders during the second processing. Although it could improve the performance of the recycled material to a certain extent, the improvement effect on the tear strength was particularly poor under the blending use (the recycled material and the new material in a ratio of 10:90 - 40:60).

[0027] Furthermore, the splines obtained by adding chain extenders during the above-mentioned second processing were crushed and subjected to GPC analysis. It was found that the GPC was bimodal. Compared with the respective corresponding peaks in the GPC of the mixture of the recycled material and the new material before processing, the molecular weight of the GPC increased, and the molecular weight distribution also increased. From this, it was inferred that some chain extenders reacted with the new material and did not play the role of reinforcing the recycled material.

[0028] In order to better reinforce the performance of the recycled material, the present invention adds a chain extender during the first processing, and chain extension occurs during the first processing, so that the molecular weight and viscosity of the obtained recycled material are close to those of the new material. Under this condition, when the recycled material and the new material are mixed for the second processing, the mixing situation in the product spline is improved to a certain extent, and the mechanical strength, especially the tear performance, is significantly improved, and can be close to or even reach the injection-molding result under the same conditions of the new material.

[0029] Furthermore, the method of the present invention can be extended to other processing methods such as extrusion and blow molding, and there is no obvious difference in principle.

[0030] The method of the present invention adds a chain extender during the processing step, increases the molecular weight and viscosity of the recycled polyester polymer, improves the molecular weight and performance of the recycled material, etc., and can prevent and compensate for the performance loss of the recycled material caused by degradation during the processing of thermoplastic polyester elastomer products.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] Compared with the conventional processing methods in the prior art, the processing and recycling method of the thermoplastic polyester elastomer provided by the present invention improves the mechanical properties such as tear strength of the products containing recycled materials.

[0033] Surprisingly, although the original intention of the present invention is to increase the molecular weight of the recycled materials and make up for the performance loss of the products after blending the recycled materials, in terms of the actual results, the mechanical properties of the first processed products, such as tensile strength and tear strength, are also significantly improved compared with the direct processing results of the new materials without using the method of the present invention. Detailed implementation manners

[0034] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0035] Description of the testing method :

[0036] Molecular weight testing method: The mobile phase is hexafluoroisopropanol, the detector is a refractive index detector, the temperature is normal temperature (25 °C), and it is calibrated with polystyrene standard samples.

[0037] Testing method for tensile strength: GB / T 528-2009 "Vulcanized rubber or thermoplastic rubber - Determination of tensile stress-strain properties".

[0038] Testing method for tear strength: National standard GBT 529-2008 "Determination of tear strength of vulcanized rubber or thermoplastic rubber".

[0039] Description of the raw material source :

[0040] Unless otherwise specified, the raw materials used in the examples or comparative examples are all commercially available.

[0041] The thermoplastic polyester elastomer used in some examples was self-made, and the polytetramethylene ether glycol (PTMEG) used was from BASF.

[0042] Preparation Example 1:

[0043] In a 15L polymerization reactor, 3.25 kg of terephthalic acid (PTA), 3 kg of 1,4-butanediol (BDO), and 1.85 kg of polytetramethylene ether glycol (PTMEG, number average molecular weight 1000), with an addition amount of about 30% of the theoretical mass of the product to be prepared, 45 g of antioxidant (BHT), and 4 g of tetrabutyl titanate were added.

[0044] The reaction vessel was purged with nitrogen three times and then gradually heated to 220 °C at 80 kPa (absolute pressure) for an esterification reaction, which took 180 - 240 minutes. After the water output slowed down (about 1600 g), the internal temperature of the reaction vessel was raised to 245 °C, and the pressure was reduced to below 50 Pa in about 30 minutes. The polycondensation reaction was continued for 60 - 120 minutes. After observing that the torque of the reaction vessel rose to the target value, the target polyester elastomer was obtained, denoted as polyester A1.

[0045] Preparation Example 2:

[0046] In a 15 L polymerization reactor, 2.5 kg of terephthalic acid (PTA), 2.5 kg of 1,4 - butanediol (BDO), and 2.21 kg of polytetramethylene ether glycol (PTMEG, number - average molecular weight 2000) were added. The addition amount was about 45% of the theoretical mass of the product to be prepared. 55 g of antioxidant (1010) and 3.5 g of tetrabutyl titanate were added.

[0047] The reaction vessel was purged with nitrogen three times and then gradually heated to 220 °C at 80 kPa (absolute pressure) for an esterification reaction, which took 180 - 240 minutes. After the water output slowed down (about 1300 g), the internal temperature of the reaction vessel was raised to 245 °C, and the pressure was reduced to below 50 Pa in about 30 minutes. The polycondensation reaction was continued for 90 - 150 minutes. After observing that the torque of the reaction vessel rose to the target value, the target polyester elastomer was obtained, denoted as polyester A2.

[0048] Injection molding conditions :

[0049] Example 1, Comparative Example 1, Example 3, Comparative Example 3: The melt temperature of the injection - molding machine was 225 °C, and the mold temperature was 45 °C.

[0050] Example 2, Comparative Example 2: The melt temperature of the injection - molding machine was 180 °C, and the mold temperature was 40 °C.

[0051] Example 1

[0052] This example provides a processing and recycling method for a thermoplastic polyester elastomer, which includes the following steps:

[0053] 1 kg of polyester A1 (new material) was mixed evenly with 15 g of butanediol diglycidyl ether, added to the hopper of an injection - molding machine, and injection - molded into test specimens. The test specimens were cut into particles less than 3 mm as recycled materials. The recycled materials were dried and stored in a dryer.

[0054] 200 g of recycled materials were mixed evenly with 800 g of polyester A1 (new material), and injection - molded into test specimens. The test results of the specimens were used as those of Example 1. The test results are shown in Table 1 and Table 2.

[0055] Example 2

[0056] This embodiment provides a processing and recycling method for thermoplastic polyester elastomer, which includes the following steps:

[0057] Mix 1 kg of polyester Hytrel 4056 (new material, DuPont, USA) with 30 g of HDI evenly, add it to the hopper of an injection molding machine, injection mold it into test specimens, and cut the test specimens into particles smaller than 3 mm as recycled materials. The recycled materials are dried and stored in a dryer.

[0058] Mix 400 g of recycled materials with 600 g of polyester Hytrel 4056 (new material) evenly, injection mold it into test specimens, and the test results of the specimens are taken as Example 2. The test results are shown in Table 1 and Table 2.

[0059] Example 3

[0060] This embodiment provides a processing and recycling method for thermoplastic polyester elastomer, which includes the following steps:

[0061] Mix 1 kg of polyester A2 (new material) with 3 g of ethylene glycol diglycidyl ether evenly, add it to the hopper of an injection molding machine, injection mold it into test specimens, and cut the test specimens into particles smaller than 3 mm as recycled materials. The recycled materials are dried and stored in a dryer.

[0062] Mix 100 g of recycled materials with 900 g of polyester A2 (new material) evenly, injection mold it into test specimens, and the test results of the specimens are taken as Example 3. The test results are shown in Table 1 and Table 2.

[0063] Comparative Example 1

[0064] Inject 1 kg of polyester A1 (new material) into test specimens, cut the test specimens into particles smaller than 3 mm as recycled materials. The recycled materials are dried and stored in a dryer.

[0065] Mix 200 g of recycled materials with 800 g of polyester A1 (new material) evenly, injection mold it into test specimens, and the test results of the specimens are taken as Comparative Example 1. The test results are shown in Table 1 and Table 2.

[0066] Comparative Example 2

[0067] Inject 1 kg of polyester Hytrel 4056 (new material, DuPont, USA) into test specimens, cut the test specimens into particles smaller than 3 mm as recycled materials. The recycled materials are dried and stored in a dryer.

[0068] Mix 400 g of recycled materials with 600 g of polyester Hytrel 4056 (new material) evenly, injection mold it into test specimens, and the test results of the specimens are taken as Comparative Example 2. The test results are shown in Table 1 and Table 2.

[0069] Comparative Example 3

[0070] 1 kg of polyester A2 (new material) was injection-molded into test specimens, and the test specimens were shredded into particles smaller than 3 mm as recycled materials. The recycled materials were dried and stored in a dryer.

[0071] 100 g of recycled materials were mixed evenly with 900 g of polyester A2 (new material) and injection-molded into test specimens. The test results of the specimens were used as Comparative Example 3. The test results are shown in Table 1 and Table 2.

[0072] Table 1 Comparison results of molecular weights of new materials, examples, and recycled materials of comparative examples

[0073] Mn Mw PDI New material A1 19757 30428 1.54 Recycled material of Example 1 19433 30739 1.58 Recycled material of Comparative Example 1 16146 25774 1.60 New material Hytrel 4056 21137 33786 1.60 Recycled material of Example 2 22304 37253 1.67 Recycled material of Comparative Example 2 18020 30104 1.67 New material A2 20737 32273 1.56 Recycled material of Example 3 17241 29663 1.72 Recycled material of Comparative Example 3 16501 27850 1.69

[0074] Table 2 Comparison results of performances of examples and comparative examples

[0075]

[0076] It can be seen from the comparison between the above examples and comparative examples that: by mixing a chain extender during the processing of the new material, the problem of decreased molecular weight after processing is significantly improved; in Example 2, when a relatively large amount of chain extender is used, the molecular weight of the recycled material can even be higher than that of the new material. For the products using the recycled materials and the new materials in admixture, their tensile strength and tear strength are significantly improved compared with the products of the comparative example recycled materials in the same proportion without mixing a chain extender during the processing of the new material. The tensile strength of the recycled product in Example 3 is 24 MPa, reaching the same level as the new material, and the tear strength is 84 kN / m, close to 85 kN / m of the new material, and both are better than those of the comparative example (23 MPa and 78 kN / m).

[0077] The above description of the examples is for the convenience of those of ordinary skill in the art to understand and use the invention. Those skilled in the art can obviously make various modifications to these examples easily and apply the general principles described herein to other examples without creative labor. Those skilled in the art should be able to simply infer that the above processing method can also affect other performances, and the advantages and disadvantages of the above processing method can be found through corresponding performance tests and adjusted flexibly accordingly. For example, the melt index of the recycled material in Example 2 is close to that of the new material and much higher than that of the recycled material in Comparative Example 2; the elongation at break of Comparative Example 2 is about 750%, while the elongation at break of Example 2 is about 560%, lower than that of the comparative example.

[0078] The present invention is not limited to the above examples and the above mechanical properties. Modifications and improvements made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A processing and recycling method for thermoplastic polyester elastomer, comprising the following steps: The thermoplastic polyester elastomer is mixed with a chain extender for the first processing; The recycled material obtained after the first processing is pulverized and mixed with virgin material in a mass ratio of 10:90 - 40:60 for the second processing; Among them, the chain extender refers to a compound containing more than 2 functional groups capable of reacting with hydroxyl groups or a mixture of such compounds. Preferably, the average functionality of the chain extender is 2 - 3.

2. The method according to claim 1, wherein 0.3 - 3 parts by mass of the chain extender is added per 100 parts by mass of the thermoplastic polyester elastomer.

3. The method according to claim 1, wherein This method further includes: before the second processing, adding a chain extender to the mixture of the recycled material and virgin material.

4. The method according to claim 3, wherein 0.3 - 3 parts by mass of the chain extender is added per 100 parts by mass of the mixture of the recycled material and virgin material.

5. The method according to claim 1 or 2, wherein The functional group capable of reacting with hydroxyl groups is an epoxy group and / or an isocyanate group.

6. The method according to claim 5, wherein The functional group capable of reacting with hydroxyl groups is an epoxy group. Preferably, the chain extender is one or a combination of two or more of bisphenol A diglycidyl ether, ethylene glycol diglycidyl ether, and butanediol diglycidyl ether.

7. The method according to claim 5, wherein The functional group capable of reacting with hydroxyl groups is an isocyanate group. Preferably, the chain extender is one or a combination of two or more of dimethylene polyphenyl polyisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

8. The method according to claim 1, wherein The first processing includes injection molding and / or extrusion; The second processing includes injection molding and / or extrusion.

9. The method according to claim 1, wherein The average functionality of the chain extender is 2.

10. The method according to claim 1, wherein The molecular weight of the chain extender ≤ 1000.

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